A number of inventions are directed to the recovery of hydrocarbons from an underground reservoir or formation.
Canadian Patent No. 1,130,201 (Butler) teaches a thermal method for recovering normally immobile oil from a tar sand deposit utilizing two wells, one for injection of heated fluid and one for production of liquids. Thermal communication is established between the wells and oil drains continuously by gravity to the production well where it is recovered.
U.S. Pat. No. 6,257,334 (Cyr. et al.) teaches a thermal process for recovery of viscous oil from a subterranean reservoir. A pair of vertically spaced, parallel, co-extensive, horizontal injection and production wells and a laterally spaced, horizontal offset well are provided. The injection and production wells are operated as a Steam-assisted Gravity Drainage (SAGD) pair. Cyclic steam stimulation is practiced at the offset well. The steam chamber developed at the offset well tends to grow toward the steam chamber of the SAGD pair, thereby developing communication between the SAGD pair and the offset well. The offset well is then converted to producing heated oil and steam condensate under steam trap control as steam continues to be injected through the injection well.